At the opening of “Three Trips Around the Block,” a scorching 15-year survey of work by Rico Gatson at Exit Art, people were lining up to stick their heads through the bottom of a box hanging from the ceiling. Titled Two Heads in a Box (1994), this confrontational video installation is the show’s earliest work. Imprisoned behind three bars inside its black interior is a movie that features Gatson’s dark face illuminated by fiery red light and adorned with a white clown nose, a painted white beard and a huge white paper bowtie. Inverting Al Jolson's racist early-20th-century blackface performances, Gatson repeatedly intones Jolson's trademark song, Let Me Sing and I'm Happy, until he is ready to drop.